We all know that a day on planet Earth lasts 24 hours – except that it is not. It’s actually a few fractions of a second longer, which is why we have February 29 every four years. Yet the Earth is not a clock, and the actual length of a day may vary slightly. Scientists now say the days have started to get shorter because the Earth is spinning faster, which could require additional, potentially confusing, adjustments.
Until you’re stressed out by another existential threat to the future of the planet, scientists don’t believe that increasing the rate of turnover is a danger. The mechanisms of this effect are well understood. Factors like lunar gravity, snow levels, and mountain erosion can affect the speed of the globe. The effect is that the days can be a few milliseconds shorter or longer than the number 84,400 that we use to track time.
Over the past several decades, the availability of precise atomic clocks has enabled humanity to make more precise adjustments to our measurement of time. For example, on several occasions we have added a “leap second” to keep the clocks aligned outside of the traditional leap year adjustment. Since we started measuring time like this, the length of days has tended to get longer, usually by a fraction of a millisecond. However, this trend has now reversed.
Scientists note that the days of last year were rather short with the same small margins. However, July 19 was a significantly shorter day, with 1.4602 milliseconds below normal. The previous record for the shortest day was set in 2005, but it was broken 28 times in 2020.
If this trend continues, we may very well need a negative jump second in the next few years to keep our clocks in sync with “real time”. It would be a first because all the previous adjustments added time. While it’s impossible to say for sure that this acceleration will continue, most scientists believe it will. Either way, the faster turnaround itself isn’t a problem – the causes could be, however. Some began to wonder aloud whether large-scale changes due to global warming have started to have a noticeable impact on rotation. Shaving a few milliseconds a day won’t hurt anyone, but it’s not really a good sign.